# Ugly solution to https://news.ycombinator.com/item?id=40989044
$ cat testrun.py
import sys
prio1ops = ('*', '/')
prio2ops = ('+', '-')

def compute(tokens):
    while True:
        resolveAt = None
        for i, token in enumerate(tokens):
            # this can be done more elegantly if prio1 and -2 are an array-like type: TODO
            if token in prio1ops:
                resolveAt = i
                break
        if resolveAt is None:
            break
        else:
            if i == 0 or i == (len(tokens) - 1):
                print('operator at the start or end?', tokens)
                return False
            # so tempting to use eval here, since this is ugly, but not sure what the better solution is
            if tokens[i] == '/':
                tokens[i - 1] = tokens[i - 1] / tokens[i + 1]
            if tokens[i] == '*':
                tokens[i - 1] = tokens[i - 1] * tokens[i + 1]
            # so we modified index-1, then delete index and index+1
            del tokens[i]
            # because it shifts, we need to remove the index position twice
            del tokens[i]

    # Copied from the whileTrue above, TODO really should merge this into DRY...
    while True:
        resolveAt = None
        for i, token in enumerate(tokens):
            if token in prio2ops:
                resolveAt = i
                break
        if resolveAt is None:
            break
        else:
            if i == 0 or i == (len(tokens) - 1):
                print('operator at the start or end?', tokens)
                return False
            # so tempting to use eval here, since this is ugly, but not sure what the better solution is
            if tokens[i] == '+':
                tokens[i - 1] = tokens[i - 1] + tokens[i + 1]
            if tokens[i] == '-':
                tokens[i - 1] = tokens[i - 1] - tokens[i + 1]
            # so we modified index-1, then delete index and index+1
            del tokens[i]
            # because it shifts, we need to remove the index position twice
            del tokens[i]

    if len(tokens) != 1:
        print('Resolved the operators, but we are left with more than one token?', tokens)
        return False

    return tokens[0]


for line in sys.stdin:
    line = line.replace(' ', '').strip()
    charssofar = ''
    tokens = []
    for char in line:
        if char in prio1ops + prio2ops:
            tokens.append(float(charssofar))
            charssofar = ''
            tokens.append(char)
        else:
            charssofar += char
    if len(charssofar) < 1:
        print('ends in an operator?')
        continue
    # TODO wrap float interpreting in try-catches
    tokens.append(float(charssofar))

    print(line, '=', compute(tokens))


$ cat testset
1 + 1
1 * 2
1 + 2 * 2
1-1
1/2
1+2/2


$ python3 testrun.py <testset
1+1 = 2.0
1*2 = 2.0
1+2*2 = 5.0
1-1 = 0.0
1/2 = 0.5
1+2/2 = 2.0